The proliferation of wireless communication interfaces in mobile and stationary devices rendered the frequency spectrum scarce. Efficient use of allocated bandwidth for communication is a critical issue for the viability of wireless communication systems.
Frequency Division Multiple Access (FDMA) is a widely used method for allowing multiple transmitters access to a common wireless channel. An example is cellular telephony where multiple mobile users access the same base station. Specifically, FDMA was recently adopted for uplink in the Long Term Evolution (LTE) extension of the Universal Mobile Telecommunication Systems (UMTS) standard.
The use of Joint Constellation Multiple Access (JCMA) is known. US patent application 20090135926 is believed to represent the most relevant prior art. US patent application 20090135926 is incorporated herein by reference
The following documents are believed to represent further relevant prior art:                J. G. Proakis, Digital Communication, McGraw Hill, 3rd edition, 1995.        T. M. Cover and J. Thomas. Elements of Information Theory. John Wiley and Sons Inc., second edition, 2006.        A. Goldsmith, Wireless Communications, Cambridge University Press, 2006.        C. Johnson, Radio Access Networks for UMTS, Wiley, 2008.        G. R. Tsouri and D. Wulich, “Securing OFDM over Wireless Time-Varying Channels using Sub-Carrier Over-Loading with Joint Signal Constellations”, Eurasip Journal on Wireless Communications & Networking, 2009.        
In the classical FDMA approach the total frequency spectrum is divided into sub-bands. The receiver allocates a sub-band to each transmitter, and each transmitter has exclusive use of its allocated sub-band. This converts the allocated total bandwidth into a set of orthogonal channels connecting the transmitters and receiver.
JCMA suggests coupling N multiple transmitters under a Superposition Modulation (SM) scheme. This allows the joining of their multiple sub-bands to a single sub-band N times larger than an original sub-band. The large bandwidth would allow transmission at a rate N times larger than the original rate. However, the energy per transmitted symbol would decrease by a factor of N as well, resulting in an increase of the Bit Error Rate (BER) upon decoding at the receiver. The increase in BER would be mitigated by applying source coding prior to transmission and by synchronizing the transmitters to form a superimposed constellation which is robust to noise at the receiver. Applying coding would result in throughput decrease. If the decrease in throughput due to coding is less than the increase in transmission rate due to bandwidth expansion, the throughput with synchronized SM would be larger than the throughput of classical FDMA.
As described above, JCMA is based on synchronous Superposition Modulation (SM) and coding for increasing the spectral efficiency of practical FDMA systems. SM is known to achieve maximal aggregated capacity. However, SM is largely avoided under the premise that capacity increase offered by SM is not substantial compared to the complexity involved in obtaining accurate synchronization and power control required for its operation.
There is thus a recognized need for, and it would be highly advantageous to have, a communication system, and particularly a JCMA communication system having increased capacity, preferably by optimizing the immunity of the constellation used to SNR.